I. Field of the Invention
The present invention relates generally to position sensors and, more particularly, to an inductive position sensor.
II. Description of Related Art
In automotive vehicles, the throttle pedal has traditionally been mechanically connected to the engine throttle by a cable. In more modern vehicles, however, a throttle position sensor is mechanically connected to the pedal and generates an electrical output signal indicative of the degree of depression of the throttle pedal. Such systems are oftentimes termed “fly-by-wire” systems.
In one type of throttle position sensor, a transmitter or exciter coil is excited by a high frequency source so that the transmitter coil generates electromagnetic radiation. This transmitter coil, furthermore, is arranged in a circular pattern although other pattern configurations may alternatively be used.
A receiver coil is also disposed in the position sensor in close proximity to the transmitter coil. Consequently, upon energization of the transmitter coil the receiver coil generates an output signal due to inductive coupling between the transmitter and the receiver coil.
Unlike the transmitter coil, however, the receiver coil includes a first loop and a second loop which is oppositely wound from the first loop. Consequently, the inductive coupling between the transmitter coil and the first loop of the receiver coil generates a voltage opposite in polarity from the voltage induced by the transmitter coil in the second loop of the receiver coil. Therefore, the receiver output signal is a combination or sum of the voltage signals from the first and second loops of the receiver coil.
In order to generate an output signal representative of the position of the throttle, a coupler element is rotatably mounted to the position sensor and rotates in synchronism with the depression and release of the throttle pedal. This coupler element, furthermore, is constructed of a material which conducts the electromagnetic radiation emitted by the transmitter coil. This coupler element overlies a portion of both the transmitter and the receiver coils. Consequently, upon movement or rotation of the coupler element, the inductive coupling between the transmitter and tie first and second loops of the receiver coil is varied. This in turn produces an output signal from the receiver coil which varies as a function of the angular position of the coupler element and thus the angular position of the throttle pedal which is mechanically coupled to the coupler element.
If the coupler element is precisely concentric with the transmitter and receiver coils, and if the space between the coupler element and the transmitter and receiver coils remains constant during the entire movement of the coupler element, the output from the receiver coil provides a precise indication of the angular position of the coupler element and thus the angular position of the throttle pedal. In practice, however, manufacturing tolerances during the manufacture of the throttle position sensor oftentimes produce a throttle position sensor in which the coupler element is not precisely concentric with the transmitter and receiver coils and/or the gap spacing between the coupler element and the receiver and transmitter coils varies somewhat from the desired gap spacing.
Different strategies have been employed to compensate for lack of concentricity between the pivotal axis of the coupler element and the axis of the transmitter and receiver coils. These strategies, however, have not been adequate to compensate for variations in the gap spacing between the coupler element and the transmitter and receiver coils to meet the accuracy requirements of the throttle position sensor.